JPH07120286A - Heating resistor for thermal air flowmeter - Google Patents

Abstract

PURPOSE:To obtain a heating resistor having a small measuring variance and stable quality. CONSTITUTION:The heating resistor for a thermal air flowmeter has a structure in which, when a groove is provided on a circumferential surface of the bore of a pipe 1 and leads 2 are adhered to its both ends, the leads 2 are mounted at the center of the bore of the pipe with the groove used for positioning. Since the adhering operation of the lead 2 to be adhered to the pipe 1 is stabilized, its measuring variance becomes small, and the resistor having a stable quality is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a heating resistor of an air flow meter, and more particularly to a thermal air flow meter using the heating resistor.

[0002]

2. Description of the Related Art As a structure of a heating resistor, a support made of an insulator is formed by a cylindrical pipe, lead wires are adhered to both ends of the support, and the resistor is spirally wound around the pipe. As an example of coating the surface with glass, there is JP-A-60-60521. However, when bonding the lead wire to the pipe, if the difference between the inner diameter of the pipe and the outer diameter of the lead wire is large, the lead wires will be fixed at offset positions, and the left and right lead wires will become heating resistors that do not lie on the same axis Could occur.

[0003]

SUMMARY OF THE INVENTION The present invention provides a heating resistor for a thermal air flow meter which improves the workability of the heating resistor lead wire insertion work and improves the positioning accuracy of the lead wire inserted into the pipe. The purpose is to provide.

[0004]

This is achieved by providing a concave groove on the inner circumferential surface of the pipe formed by the lead wire of the heating resistor and the insulator holding the resistor.
The shape of the groove can also be achieved by forming a rectangular, triangular, or semicircular cross-sectional shape.

Alternatively, it can be achieved by providing chamfers on the inner or outer diameter side circumferences of both end faces of the pipe.

[0006]

The heating resistor has a structure in which leads are adhered and fixed to both ends of a pipe formed of an insulating material. When bonding the pipe and the lead wire made of metal, glass, an inorganic adhesive, or a conductive adhesive is usually used. Since these adhesives are fired at a high temperature, the air inside the pipe expands and pushes the adhesive at both ends of the pipe to escape to the atmosphere, so that the wetness of the adhesive after firing is poor.

Also, after the adhesive has once melted during firing,
If the difference between the inner diameter of the pipe and the outer diameter of the lead is large due to re-solidification, when the adhesive melts, the lead wire is pulled by the surface tension to the one having a large amount of the adhesive, and the lead wire is fixed while being eccentric.

The present invention improves the above-mentioned poor wettability of the adhesive and the eccentricity of the lead wire. By providing a concave groove on the circumferential surface of the pipe on the inner diameter side, the lead wire is always fixed at the center position of the inner diameter of the pipe. At this time, the groove is filled with an adhesive to bond and fix the pipe and the lead. The outer circumference of the concave surface is a positioning for matching the center of the inner diameter of the pipe with the center of the lead wire. The concave groove provided in the pipe inner diameter portion is also effective as a ventilation hole. As described above, the adhesive may have poor wettability because there is no vent hole for letting out the expanded air inside the pipe when the adhesive cures, but among the several concave grooves, for example, one place is a vent hole. The wettability of the adhesive is improved and stable bonding work can be performed, and the quality is stable.

Further, by providing chamfers on the inner diameter portions of both ends of the pipe, workability is dramatically improved. As a guide for inserting the lead wire into the end face of the pipe, it is advantageous to use it in combination with the pipe having the above-mentioned recessed groove to cope with an automatic machine.

[0010]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an external projection view of a heating resistor of the present invention,
2 and 3 are other embodiments of the invention shown in FIG. 1, FIG. 4 is a sectional structure view of a heating resistor of the present invention, and FIG. 5 is a sectional structure view of a thermal air flow meter using the present invention. is there.

The structure of the heating resistor of the present invention will be described with reference to FIG. Reference numeral 1 is a pipe-shaped support body that holds a lead wire and a resistor formed of an insulator such as alumina or zirconia. Reference numeral 2 is a lead wire fixed to both ends of the pipe 1 by a glass adhesive 3. The resistor 4 is formed of a winding wire or a thin film and is wound around the pipe 1 in a spiral shape to form a resistor or is subjected to spiral trimming. Furthermore, an overcoat glass 5 is applied to cover the entire surface of the resistor.

FIG. 1 shows a heating resistor of the thermal type air flow meter of the present invention. This is a structure in which a concave groove 6 is provided on the inner circumference of the pipe 1. FIG. 2 shows a structure in which the concave groove 6 on the inner circumference of the pipe 1 has a triangular cross-sectional shape. FIG. 3 shows the pipe 1
The concave groove 6 on the circumference of the inner diameter has a semicircular cross-sectional shape.

By providing a concave groove on the circumferential surface on the inner diameter side of the pipe, the lead wire is always fixed at the center position of the inner diameter of the pipe. At this time, the groove is filled with an adhesive to bond and fix the pipe and the lead. The outer circumference of the concave surface is a positioning for matching the center of the inner diameter of the pipe with the center of the lead wire. The concave groove provided in the pipe inner diameter portion is also effective as a ventilation hole. As described above, the adhesive may have poor wettability because there is no vent hole for letting the expanded air inside the pipe escape when the adhesive cures.However, among the several concave grooves, for example, one hole may be a vent hole. The wettability of the adhesive is improved and stable bonding work can be performed, and the quality is stable.

FIG. 4 shows a structure in which the lead wire 2 is inserted into the chamfered portion 7 whose inner circumference is chamfered. Workability is dramatically improved by providing chamfers on the inner diameters of both ends of the pipe. As a guide for inserting the lead wire into the end face of the pipe, it is advantageous to use it in combination with the pipe having the above-mentioned recessed groove to cope with an automatic machine.

FIG. 5 shows an embodiment of a thermal air flow meter using the heating resistor of the present invention. 8 is the heating resistor of the present invention,
Reference numeral 9 is a temperature sensitive resistor for measuring the temperature of intake air, 10 is a body accommodating an air passage and a drive circuit, and 11 is a drive circuit for converting the air flow rate from the heating resistor 8 and the temperature sensitive resistor 9 into an electric signal. is there. As described above, by installing the heating resistor 8 of the present invention in the air passage, it is possible to provide a thermal air flow meter with high measurement accuracy.

[0017]

According to the present invention, there is an effect that it is possible to provide a heating resistor for a thermal type air flow meter which has good workability and is stable in quality with little variation in lead wire adhesion.

[Brief description of drawings]

FIG. 1 is an external projection view of a heating resistor of the present invention.

FIG. 2 is a sectional view of an example.

FIG. 3 is a sectional view of an example.

FIG. 4 is a sectional structural view of a heating resistor of the present invention.

FIG. 5 is a cross-sectional structure diagram of the thermal air flow meter of the present invention.

[Explanation of symbols]

1 ... Pipe, 2 ... Lead wire, 3 ... Glass adhesive, 4 ... Resistor, 5 ... Overcoat glass, 6 ... Groove, 7 ... Chamfered portion, 8 ... Heating resistor, 9 ... Temperature sensitive resistor, 10 … Body, 11… Drive circuit.

Claims (3)

[Claims] 1. A heating resistor used in a thermal air flow meter for heating a heating resistor to a predetermined temperature and detecting an air flow rate from a heating current value required at this time. A thermal air flow rate characterized in that a groove is provided on the circumferential surface on the pipe inner diameter side of the pipe-shaped support formed of an insulator such as alumina or zirconia to be held, and positioning is performed when the lead wire is inserted. Heating resistor of the meter. 2. A heating resistor for a thermal air flow meter according to claim 1, wherein the pipe-shaped support has a triangular, semi-circular or quadrangular concave shape. 3. The heating resistor for a thermal air flow meter according to claim 1, wherein chamfers are provided on the inner peripheral portions of both end faces of the pipe-shaped support.